In current lighting applications, energy efficiency is a more and more important subject. One possible way to reduce the energy consumption of a lighting system is to switch off or dim one or more light sources thereof when no object (i.e. person or vehicle) is present in a space, and conversely to switch on the light(s) when an object moves into the space. In order to do this, the presence of an object in the relevant space has to be detected. Different types of motion sensors are currently in use.
There is a strong need for sensor-driven light control systems, because of their advantage of bringing down the energy consumption of the light source(s) thereof, and thereby improving cost-savings, and life-time of the light source(s).
In a typical sensor driven light control infrastructure a multitude of motion sensors (Passive Infra-Red (PIR) sensors, Image sensors, Radar sensors, etc.) are typically installed in the lighting infrastructure for various sensing requirements. These sensors are capable of similar sensing functionalities but at different levels of accuracy/robustness, and also consume different levels of energy/power. For example, known image sensors are capable of processing captured images to differentiate between different kinds of sensed motion, e.g., between a passing cyclist and a tree blowing in the wind. Thus such a motion sensor can be used to infer the absence of vehicles, cyclists and/or pedestrians, and dim-down luminaires accordingly, even in the presence of other types of sensed motion. However, this high level of accuracy comes at a cost. In particular image sensors typically consume more energy than other types of motion sensor. For instance, an image sensor consumes more energy than an ultrasonic sensor, which in turn consumes more energy than a PIR sensor.
In traffic density (object count over time) based lighting applications, known solutions use a less accurate and more energy efficient sensor to detect objects during periods of lower traffic density and use a more accurate and less energy efficient sensor to detect objects during periods of higher traffic density.